A method for preparing aliphatic/aromatic copolyester resins and composition containing the same are known in the art and the aliphatic/aromatic copolyester resins have been studied for their extended application and their processabilities and mechanical and physical properties for several decades.
For example, U.S. Pat. No. 4,094,721 (Jun. 13, 1978) and U.S. Pat. No. 4,966,959 (Oct. 30, 1996) disclose an aliphatic/aromatic copolyester resin composition and its melting point and the other properties wherein said copolyester resin composition has 40 mole % of aromatic acid moieties and the remaining aliphatic acid moieties in the molecular structure of copolyester and a total sum of said acid moieties is 100 mole % and wherein said copolyester is produced by reacting the acid moieties with a mixture of 1,4-butanediol and the others as a glycol moiety.
The above prior patents particularly disclose the range of composition of aliphatic acid components and aromatic acid components, etc. which can produce biodegradable aliphatic/aromatic copolyester in the aliphatic/aromatic copolyester resin composition and disclose in detail the melting point, inherent viscosity, etc. and some general features of said aliphatic/aromatic copolyester depending on composition of the components used.
All plastics can be used as an adhesive, if required, by using the property of plastics that allows them to be cured on cooling after melting. The above aliphatic/aromatic copolyester can be also used as a hot-melt adhesive (see, U.S. Pat. No. 4,401,805 issued on Aug. 30, 1983 and U.S. Pat. No. 4,328,059 issued on May 4, 1982). The aliphatic/aromatic copolyester exhibits tackness depending on the kind and the number of the used components. According to U.S. Pat. No. 4,966,959 (1990, Cox. A. Heyer. M. F.), the glycol components to be used must two dialcohol components in order to make an aliphatic/aromatic copolyester with tackiness.
The publication of Korean patent application no. 10-1993-0701622 discloses that although the tackness of aliphatic/aromatic copolyester according to the above prior art results in a problem in forming a plastic article, the above problem was overcome by using a single component other than a mixture of at least two components as a glycol component used in preparing aliphatic/aromatic copolyester.
However, it is well known by a person skilled in the art that it is possible to remove the tackness by adjusting the number and the kind of the components used in preparing the aliphatic/aromatic copolyester. U.S. Pat. No. 4,328,059 discloses a method for preparing aliphatic/aromatic copolyester by solely using dialcohol. In addition to the above patent literatures, Journal of Macromolecule, SCI-Chem A-23(3), 1986, P393-409 discloses that aliphatic/aromatic copolyester composition has biodegradable property when aliphatic acid component at least a portion of aliphatic acid components exists. However, aliphatic/aromatic copolyester produced by the method as stated above still has inferior processibility and mechanical property, etc. to commonly-used resins such as polyethylene, polypropylene, polystyrene and the like. Accordingly, in order to resolve the problem in connection with the aliphatic/aromatic copolyester, extensive studies have been performed.
For example, the publication of Korean patent application no. 10-1999-7002353 discloses a method of preparing aliphatic/aromatic copolyester by oligomerising chain extender such as diisocyanate or hexamethylenediisocyanate to control the content of NCO, i.e. functional group for chain extension and using the oligomerized chain extender. This method uses multifunctional group and isocyanate in order to insure processibility and mechanical property by making the resulting copolyester to have high molecular weight. However, due to the isocyanate, stability of the manufacturer can be affected in preparing copolyester and it is detrimental to the environment and human body. In addition, the above method has disadvantage in view of economy.
The publication of Korean patent application no. 10-1997-2703252 discloses a method of preparing aliphatic/aromatic copolyester resin by using a sulfonate compound or a compound having at least three functional groups which can result in ester. However, this method makes the reaction time short and makes the average molecular weight high, but molecular weight distribution of the aliphatic/aromatic copolyester composition is broad and a large amount of low molecular weight copolyester are resulted. The aliphatic/aromatic copolyester resin produced by the above method is pyrodegradable and an article prepared by the above copolyester resin has weak moisture resistance to the moisture in the atmosphere, thereby lowering durability of the article.
The invention of Korean patent application no. 10-1997-0703253 uses dihydroxy compound containing ether functional group to prepare aliphatic/aromatic copolyester resin. This invention used polyol represented by polyethyleneglycol in the example. In this case, esterification and polycondensation reactions is not easily performed and thus not only it is difficult to obtain aliphatic/aromatic copolyester with high molecular weight but also the reaction time increases and it is disadvantage in view of preparing cost.